Tribological Performance of UHMWPE and PFPE Coated Films on Aluminium Surface

A thin layer of Ultra High Molecular Weight Polyethylene (UHMWPE) or UHMWPE + PFPE is coated onto cylindrical aluminium (Al) pin (4.6 mm diametre) surface with the aim of providing wear resistant coating on this soft and tribologically poor metal. The coefficient of friction and wear life of the coated samples are investigated on a pin-on-disk tribometre under different normal loads (394–622 g) and two sliding speeds (0.1 and 0.31 m/s) against uncoated Al disk as the counterface. Both coatings provide coefficient of friction values in the range of 0.02–0.2 as compared to 0.4–1.0 for uncoated Al. There is tremendous improvement in the wear life of the pin, with UHMWPE + PFPE film giving wear life approximately twice to thrice higher than that with only UHMWPE film. A thin polymer film is transferred to the disk surface during sliding providing very long-term wear life (continuous low coefficient of friction) despite visual removal of the film from the pin surface. The present films will have applications in gears and bearings as solid or boundary lubricants for automotive and aerospace component.     

模拟矿井环境下的PEEK/SiO2/CF-MoS2复合材料摩擦行为研究*

为改善聚醚醚酮（PEEK）在矿井工况下的摩擦性能,选用纳米二氧化硅（SiO2）、二硫化钼（MoS2）和短切碳纤维（CF）为增强填料制备PEEK/SiO2/CF-MoS2复合材料,并探究PEEK/SiO2/CF-MoS2复合材料在不同工况条件下的滑动与滚动摩擦学性能;通过模拟滚轮罐耳在矿井环境下的运行方式,分析其磨损形貌和磨损机制。结果表明：PEEK/SiO2/CF-MoS2复合材料在不同载荷条件下均具有良好的减摩和耐磨特性;滑动摩擦在水介质工况下及滚动摩擦在干摩擦工况下,复合材料的摩擦因数和磨损率最低,其磨损机制均以磨粒磨损为主。与矿井常用的聚氨酯材料的对比,PEEK/SiO2/CF-MoS2复合材料的摩擦学性能更为优异。     

A novel method of using continuous tribo-electrification variations for monitoring the tribological properties between pure metal films

The traditional method of using the continuous variation of the friction coefficient with sliding distance to monitor the tribological properties between the contacts of soft metal films is generally low in sensitivity. This paper proposed the novel method of using instead the continuous variation of tribo-electrification voltage. This method was investigated experimentally for the dry friction sliding of iron on copper coated with a thin film of tin and was shown to be much superior to the traditional method in terms of sensitivity and ease of implementation. Moreover, it was observed that the continuous variations of the friction coefficient with sliding distance was very unstable but remained positive, making it indiscriminative for monitoring the tribological properties between the hard metal films. The continuous variations of the tribo-electrification voltage, on the other hand, showed either positive or negative polarity depending on the metal pairs, which allowed the identification of the surface where friction had occurred as well as the sliding surface. Finally, two continuous models to represent the tribo-electrification mechanisms for iron sliding against copper coated with a thin film of tin or nickel at different normal loads were proposed.     

极端工况下不同水润滑轴承材料摩擦磨损性能对比研究

在干摩擦工况下模拟水润滑膜严重破坏的极端情况,研究未经改性聚四氟乙烯(PTFE)、超高分子量聚乙烯(UHMWPE)和聚醚醚酮(PEEK)3种材料在不同转速和载荷下的摩擦磨损性能。结果表明:干摩擦工况下UHMWPE材料具有优异的耐磨性和良好的自润滑性能,压力对摩擦因数影响比转速大;PTFE材料具有稳定的摩擦因数,压力和转速对摩擦因数影响明显,耐磨性较差;PEEK材料摩擦因数较大,且相对容易受转速和压力变化的影响,但具有良好的耐磨性能。综合分析,在极端工况下UHMWPE的适应能力最好,PEEK次之, PTFE最差。     

Effect of Blowing Air and Floating Sand-dust Particles on the Friction and Wear Behavior of PTFE, UHMWPE and PI

The friction and wear behaviors of polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), and polyimide (PI) have been comparatively evaluated under dry sliding, blowing air, and simulated sand-dust conditions. The tribological tests were conducted on an improved block-on-ring test rig equipped with an attachment for simulating the sand-dust environment. The reason for the difference in the tribological behavior of these polymers under the three test conditions was also comparatively discussed, based on scanning electron microscopic examination of the worn polymer specimens and counterfaces. Under blowing air conditions, the decrease of the contact temperature produced by blowing air led to the increase in the shearing strength of the sliding surface when compared with dry sliding conditions and hence to cause an increase in the friction coefficient and a remarkable decrease in the wear rate of PTFE and UHMWPE. On the contrary, blowing air produced a decrease in the friction coefficient of PI because of the formation of transfer film on the counterfaces, and an increase in the wear rate, because the blowing air considerably promoted the transfer of PI onto the counterfaces when compared with dry sliding conditions. Both PTFE and UHMWPE registered the lowest wear rate under sand-dust conditions, owing to the tribolayer formation on the worn surfaces, while PI exhibited the highest wear rate because no tribolayer was formed during the abrasive wear process.     

Tribological Behavior of PTFE Composites Filled with PEEK and Nano-Al2O3

In this study, the tribological properties of polytetrafluoroethylene (PTFE) composites filled with polyetheretherketone (PEEK) and nano-Al₂O₃ particles were studied using a block-on-ring wear tester. The tribological performance of the composites was affected by the experimental parameters (sliding speed, normal load, and environmental temperature) and the composites achieved a high-speed sliding friction state. The results showed that the PEEK and nano-Al₂O₃ particles significantly improved the wear resistance of the PTFE composites. In addition, the nano-Al₂O₃ particles increased the hardness of the composites and enhanced the mechanical properties to enable applications in a wider range of industrial fields. The effects of the sliding speed and normal load on the tribological properties were more significant than that of the environmental temperature. In addition, the entire wear process was divided into three stages (the initial wear stage, severe wear transition stage, and ultralow stable wear stage), according to the evolution of the tribological characteristics (wear rate, morphology of the worn surface and transfer film, and wear debris morphology).     

Effects of sliding velocity and applied load on the tribological mechanism of amorphous poly-ether–ether–ketone (PEEK)

In this work, the effects of sliding velocity and applied load on the tribological characteristics, i.e. friction coefficient and wear rate, of an amorphous poly-ether–ether–ketone (PEEK) coating was examined. Friction tests were performed on a ball-on-disc apparatus. Based on analyses of the worn tracks, a comprehensive attempt is made to approach the tribological mechanism of amorphous PEEK. A hypothesis is proposed that the tribological behaviour of the amorphous PEEK is closely related to its viscoelastic behaviour. The sliding velocity plays significant roles on the tribological characteristics by influencing the interface temperature and strain rate of the PEEK surface layer involved in the friction process. The applied load influences the tribological performance by varying the strain range in the surface layer.     

Tribological Behaviour of Polymeric Coatings: II. SCF‐Reinforced PEEK Nanocomposite Systems

This paper focuses on coatings based on poly(ether ether ketone) (PEEK) applied to metal substrates and their tribological investigation. Short carbon fibres (SCF), graphite, and 300 nm titanium dioxide (TiO₂) and zinc sulphide (ZnS) particles were used as filler materials for the PEEK. These filler materials and their combinations were found to have a significant influence on the tribological behaviour of the corresponding PEEK compounds. One of the compounds (PEEK6) was found, especially at higher temperatures and under higher normal loads, to be a good coating material showing superior tribological behaviour. For PEEK6, a specific wear rate and a coefficient of friction (COF) lower than those for the best commercially available PEEK compound (PEEK4) were measured. For specific test parameters, PEEK6 showed a COF of less than 0.1. The tribological results were also compared with those of a conventional sliding bearing material based on poly(vinylidene fluoride) (PVDF).     

On dry sliding friction and wear behaviour of PEEK and PEEK/SiC-composite coatings

In this work, polyetheretherketone (PEEK) and PEEK/SiC-composite coatings were deposited on Al substrates using a printing technique to improve their surfaces performance. The objective of this work was to investigate coatings friction and wear behaviour. Especially, the effect of sliding velocity and applied load on coatings friction coefficient and wear rate was evaluated in range of 0.2-1.4 m/s and 1-9 N, respectively. Compared to Al substrate, the coated samples exhibit excellent friction coefficient and wear rate. For PEEK coating, under an applied load of 1 N, the increase in sliding velocity can result in decreasing of friction coefficient at a cost of wear resistance. Under a load of 9 N, however, PEEK coating exhibits the highest friction coefficient and wear rate at an intermediate velocity. These influences appear to be mainly ascribed to the influence of contact temperature of the two relative sliding parts. In most test conditions, the composite coating exhibits better wear resistance and a little higher friction coefficient. SiC reinforcement in composite coating plays a combined role. First of all, it might lead to energy dissipation for activation of fracture occurred on the interface of PEEK and the powders. Moreover, it can reduce coating ploughs and the adhesion between the two relative sliding parts.     

Sliding contacts for the pharmaceutical industry: failure analysis and dry sliding tests for the replacement of hard Cr on AISI 316L steel

Several alternatives were compared for the replacement of hard electroplated Cr coating to improve the tribological properties of the AISI 316L austenitic stainless steel for pharmaceutical packaging applications, including low temperature carburizing (LTC), thermal spray coatings (Al₂O₃-13TiO₂, WC-17Co), substitution of the AISI 301 reference counterface with polymeric materials (PTFE, UHMWPE, PEEK). In dry sliding block on ring tests, the LTC AISI 316L cylinders lead to the lowest wear rates of the AISI301 sliders under low loads (up to 10 N). When considering the polymer vs. uncoated AISI 316L couple, PEEK and UHMWPE lead to lower friction and comparable wear rates with respect to the reference couple (AISI 301 vs. Hard Cr coated-AISI 316L) in the whole range of tested loads.     

Tribological properties of Si-containing diamond-like carbon film under ATF lubricated condition

Recent years have seen a rise in social needs regarding safety and the environment, and this has placed increasing importance on product development for automotive parts that leads to smaller sizes, higher capacity, and lower costs. Diamond-like carbon (DLC) coating technology is being focused on as an effective solution to such issues.This paper reports on the tribological properties of a Si-containing diamond-like carbon film under an automatic transmission fluid (ATF) lubricated condition, which dramatically improves the performance of an electromagnetic clutch used in electronically controlled All-wheel-drive (AWD) coupling. The Si-containing DLC film maintains its rough sliding surface while simultaneously exhibiting extremely low aggression against mating materials. Thus, the boundary lubrication state of the initial friction stage is maintained, while also displaying a positive μ–v slope with excellent anti-shudder performance and a satisfactory friction coefficient as demanded by the drive train.Based on time-of-flight secondary ion mass spectrometry (TOF-SIMS) of sliding surfaces, it was speculated that the mechanism behind the good tribological properties of a sliding material coated with Si-containing DLC film under fluid lubrication are in part connected to the material properties of the DLC-Si film and an adsorbate such as a succinimide-based dispersant.     

多壁碳纳米管改性UHMWPE的热膨胀和摩擦学性能研究

为了降低摩擦副用聚合物的热膨胀系数,用多壁碳纳米管(MWCNTs)改性超高分子量聚乙烯(UHM-WPE),通过热压成型法制备MWCNTs/UHMWPE复合材料.通过测量电导率计算渗流阈值来表征分散性;用热膨胀仪(DIL)测试复合材料的热膨胀率,并在干摩擦环境下,测试不同MWCNTs含量复合材料的摩擦学性能.结果表明:通...     

PTFE基复合材料海水润滑下的摩擦学性能研究

研究碳纤维/聚四氟乙烯（CF/PTFE）、玻璃纤维/聚四氟乙烯（GF/PTFE）复合材料与氮化硅陶瓷配副在海水环境下的摩擦学性能与润滑机制,分析滑动速度对摩擦副海水润滑性能的影响规律。结果表明：在海水润滑条件下,随着滑动速度的增加,PTFE、CF/PTFE、GF/PTFE材料与Si3N4陶瓷配副时的摩擦学性能均有明显改善,摩擦因数与磨损率均呈显著降低的趋势,其中CF/PTFE复合材料表现出更为优异的摩擦学性能,在1 000 r/min滑动速度下摩擦因数低至0.026。磨损表面表征结果表明,在海水润滑条件下,PTFE基复合材料在摩擦过程中由于摩擦化学反应生成了润滑膜,可为摩擦副提供良好的润滑和减磨作用,从而减少摩擦磨损行为的发生。     

An Improved Tribological Polymer-Coating System for Metal Surfaces

Aromatic thermosetting polyester (ATSP)- and polytetrafluoroethylene (PTFE)-blended composites have been shown to exhibit improved tribological performance with low wear and low friction. In this article, pure ATSP films were coated on aluminum substrates and tested as a potential protective tribological coating. The tribological performance of this coating was tested against steel, using pure sliding sphere-on-disk experiments. A fluoroadditive powder (solid lubricant) was also added to further enhance the ATSP film wear and friction properties. For comparison, a commercially available PTFE-based coating was tested under the same conditions. Results show that the ATSP/fluoroadditive film has comparable coefficient of friction to the commercial coating, but significantly lower wear. Surface analysis techniques were employed to investigate the low-friction and low-wear mechanisms seen with the ATSP/fluoroadditive. Specifically TOF-SIMS depth-profiling showed that there is a high density of fluorine element within the wear track and penetrates well below the surface of the wear track.     

PEEK450 FC30与SiC陶瓷在海水润滑下的摩擦磨损特性研究

碳纤维增强聚醚醚酮PEEK450 FC30与工程陶瓷SiC软硬组合作为海水柱塞泵关键摩擦副备选材料,利用MCF 10摩擦磨损试验机对其在海水润滑下的摩擦磨损特性进行试验研究,探讨接触压力、滑动转速对材料磨损率和摩擦系数的影响规律。试验结果表明：在一定范围内的滑动速度、接触压力下,该摩擦副呈现出较小的磨损率和摩擦系数。当滑动速度在0.5~1.5 m/s之间,接触压力为1.33 MPa时,磨损率最小。通过扫描电子显微镜观察摩擦副磨损表层发现,在海水润滑下,SiC磨损并不明显,而PEEK450 FC30的磨损主要是以塑性涂抹为特征的粘着和SiC表面粗糙峰引起的机械犁耕。研究结果对水液压元件的选材具有十分重要的指导作用。     

Molecular Orientation, Crystallinity, and Topographical Changes in Sliding and their Frictional Effects for UHMWPE Film

This paper presents a study on the frictional anisotropy of semi-crystalline UHMWPE polymer film deposited on DLC-overcoated Si substrate. For UHMWPE film slid against a silicon nitride ball, there is a remarkable difference in the coefficient of friction between the forward and reverse directions after the slider has been initially slid against the film for certain number of cycles. The changes in the friction are greatly influenced by the initial number of sliding cycles. This frictional behavior is explained in terms of crystallinity change and molecular orientational effects on UHMWPE and micro-topographical effects due to the initial sliding. Nanoscratch test is conducted to understand the friction of the polymer film in the sliding track and the data are compared with the macroscale friction data. The results show that the friction in the reverse of the initial sliding direction is high in comparison to that in the forward direction and this behavior mainly depends upon the number of initial sliding cycles. The initial sliding cycles affect the crystallinity and molecular orientation of the film, as well as the film topography. This combined effect on the polymer film results in an anisotropic frictional behavior of the film.     

A study on tribological behaviour of transfer films of PTFE/bronze composites

Transfer films of PTFE/bronze composites with 5–30% volume content of bronze were prepared using a RFT friction and wear tester on surface of AISI-1045 steel bar by different sliding time (5–60 min). Tribological properties of these transfer films were studied using a DFPM reciprocating tribometer in a point contacting configuration under normal loads of 0.5, 1.0, 2.0 and 3.0 N. Thickness and surface morphology of the transfer films were investigated. It was found thickness of the transfer films slightly increased along with the increase of bronze content of corresponding composites. Increased sliding time of transfer film preparation is helpful to form transfer film with better ductibility and continuity, but sliding time almost has no effect on tribological properties of the transfer film. Higher bronze content in the composite improved tribological properties of the corresponding transfer film, i.e., reduced friction coefficient and prolonged wear life. All these transfer films are sensitive to load change. Their wear life becomes shorter along with the increase of load. SEM image of the worn surface show fatigue wear and adhesion wear have happened on the transfer film during the friction process. The author believe bronze in the transfer film effectively partaked in shear force applied on the transfer film and its good ductibility helped to improve tribological properties of the transfer films.     

Tribological behaviours of PA/UHMWPE blend under dry and lubricating condition

Dry-sliding and lubricated friction and wear behaviours of polyamide (PA) and ultra-high molecular weight polyethylene (UHMWPE) blend were studied using a pin-on-disc method (polymer pin sliding against a stainless steel disc) at room environment. The tribological performance of PA and UHMWPE were also investigated for the purpose of comparison. The worn surfaces were examined using a scanning electron microscope (SEM) and optical microscope. It was observed that PA specimen demonstrated highest friction coefficient, UHMWPE the lowest in both dry-sliding and lubricated sliding test. The friction of PA could be sufficiently decreased by blending with UHMWPE. Statistical analysis suggested the relationship between the wear volume loss and the sliding distance could be expressed by a linear model for dry-sliding, while a logarithmic model was determined for lubricated sliding. The difference in wear modes between both sliding series suggested that there was change in the mode of material removal process. The lower wear rate in lubricated sliding was attributed to the elastohydrodynamic or partial elastohydrodynamic lubrication through the development of a continuous lubricant film between the polymer and the counterface, while the high wear rate of the specimens, in dry-sliding test, was mainly caused by fatigue process due to the repeated action of tearing and crack-propagation.     

Characterization and tribological investigation of self-assembled lanthanum-based thin films on glass substrates

Rare-earth (RE) (lanthanum-based) thin films were prepared on hydroxylated glass substrates by a self-assembling process from specially formulated solution. Atomic force microscope (AFM) and X-ray photoelectron spectrometry (XPS) and scanning electron microscope (SEM) are used to characterize the thin films. The tribological properties of the as-prepared thin films sliding against a steel ball were evaluated on a friction and wear tester. The tribological experiment shows that the friction coefficient of glass substrate reduced from 0.85 to 0.13 after the formation of RE self-assembled film (SAM) on its surface. And the RE self-assembled film has longer wear life (2880 sliding pass). It is demonstrated that RE self-assembled film exhibited good wear resistant property. The superior friction reduction and wear life of RE films are attributed to good adhesion of the film to the substrate and special characteristic of the RE elements.     

Tribological Behavior of UHMWPE Reinforced with Graphene Oxide Nanosheets

In this article, a series of graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) composites are successfully fabricated through an optimized toluene-assisted mixing followed by hot-pressing. The mechanical and tribological properties of pure UHMWPE and the GO/UHMWPE composites are investigated using a micro-hardness tester and a high speed reciprocating friction testing machine. Also, the wear surfaces of GO/UHMWPE composites are observed by a scanning electron microscope (SEM), to analyze the tribological behavior of the GO/UHMWPE composites. The results show that, when the content of GO nanosheets is up to 1.0 wt%, both the hardness and wear resistance of the composites are improved significantly, while the friction coefficient increases lightly. After adding GO, the tribological behavior of the GO/UHMWPE composites transforms from fatigue wear to abrasive wear associated with the generation of a transfer layer on the contact surface, which efficiently reduced the wear rate of the GO/UHMWPE composites.